An instrumentation amplifier configured for providing high common mode rejection and low distortion is described. The instrumentation amplifier can include an input differential transistor pair including a first input transistor and a second input transistor and configured to receive a differential input voltage at a first feedback input and a second feedback input, and to output current mode signals. The instrumentation amplifier can include a folded cascode amplifying stage configured to receive output current mode signals provided from said input differential transistor pair, the folded cascode amplifying stage including first output terminal and a second output terminal. The instrumentation amplifier can include a plurality of feedback paths or networks, e.g., a first external gain setting circuitry comprising a first resistor feedback network and a second external gain setting circuitry comprising a second resistor feedback network.
In an example, the first resistor feedback network may include a first resistor, a second resistor and a third resistor. The first resistor is connected between the first feedback input and the second feedback input of said input differential transistor pair. The second resistor is connected between the first output terminal of the folded cascode stage and the second feedback input of said input differential transistor pair. The third resistor is connected between the second output terminal of the folded cascode amplifying stage and the first feedback input of said input differential transistor pair.
In an example, the second resistor feedback network includes a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor. The fourth resistor is connected between a first signal input and a gate terminal of the first input transistor of said input differential transistor pair. The fifth resistor is connected between the first output terminal of the folded cascode amplifying stage and a gate terminal of the first input transistor of said input differential transistor pair. The sixth resistor is connected between a second input and a gate terminal of the second input transistor of said input differential transistor pair. The seventh resistor being connected between second output terminal of a folded cascode stage and the gate terminal of the second input transistor of said input differential pair.
In an example, the instrumentation amplifier may further comprise a first output buffer and a second output buffer, the first output buffer and the second output buffer being configured to receive a differential output signal from the folded cascode amplifying stage and provide an output voltage to the first external gain setting circuitry and the second external gain setting circuitry.
In an example, the instrumentation amplifier may further comprise a current buffer stage including a pair of transistors, each of the pair of transistors being configured as a current source to a corresponding transistor of the folded cascode amplifying stage, the current buffer stage being configured to provide a portion of a sum of the output voltage to input terminals of a folded cascode stage.
In an example, a dependent current source is connected to the current buffer stage. The dependent current source is configured to provide cancellation current to input terminals of folded cascode stage.
In an example, the instrumentation amplifier further comprises a first output buffer and a second output buffer, the first and second output buffers being configured to receive a differential signal from the folded cascode amplifying stage.
In an example, a third external gain setting circuitry is proved and comprises a third resistor feedback network. The third resistor feedback network includes an eighth resistor connected between an output terminal of the first output buffer and the second feedback input of said input differential transistor pair, and a ninth resistor connected between an output terminal of the second output buffer and the first feedback input of said input differential transistor pair.
In an example, a fourth external gain setting circuitry is provided and includes a tenth resistor connected between the output terminal of the first output buffer and the gate terminal of the first input transistor of said input differential transistor pair, and an eleventh resistor connected between the output terminal of a second output buffer and the gate terminal of the second input transistor of said input differential transistor pair.
An instrumentation amplifier is described and may, comprise an input differential stage configured to receive a differential input voltage at a first and a second input and to output current mode signals, the input differential stage including a first input transistor and a second input transistor; a folded cascode amplifying stage configured to receive output current mode signals from the input differential stage; and a plurality of feedback networks operating as gain setting circuitry, wherein a first resistor feedback network of the plurality of feedback networks providing feedback to the first input transistor and the second input transistor, wherein a second resistor feedback network of the plurality of feedback networks providing feedback to inputs of the first input transistor and the second input transistor.
In an example, the first resistor feedback network includes a first resistor connected between a first feedback input and a second feedback input of the first input transistor and the second input transistor; a second resistor connected between a first output terminal of the folded cascode stage and a second feedback input of the input differential stage; and a third resistor connected between a second output terminal of the folded cascode amplifying stage and a first feedback input of the input differential stage.
In an example, the second resistor feedback network includes a first resistor being connected between a first signal input and a gate terminal of the first input transistor of the input differential stage; a second resistor being connected between a first output terminal of the folded cascode amplifying stage and a gate terminal of the first input transistor of the input differential stage; a third resistor being connected between a second input and a gate terminal of the second input transistor of the input differential stage; and a fourth resistor being connected between a second output terminal of the folded cascode stage and the gate terminal of the second input transistor of the input differential stage.
In an example, the instrumentation amplifier further comprises an output buffer configured to receive a differential output signal from the folded cascode amplifying stage and provide an output voltage to the first resistor feedback network and the second resistor feedback network.
In an example, the instrumentation amplifier further comprises a current buffer stage including a pair of transistors, each of the pair of transistors being configured as a current source to a corresponding transistor of the folded cascode amplifying stage, the current buffer stage being configured to provide a portion of a sum of output signals from the amplifier to input terminals of a folded cascode amplifying stage; and a dependent current source connected to the current buffer stage, the dependent current source being configured to provide cancellation current to input terminals of folded cascode amplifying stage.
In an example, the instrumentation amplifier further comprises a first output buffer and a second output buffer, the first and second output buffers being configured to receive a differential signal from the folded cascode amplifying stage; and wherein the plurality of feedback networks includes a third resistor feedback network.
In an example, the third resistor feedback network includes a first resistor connected between an output terminal of the first output buffer and a second input of the input differential stage; and a second resistor connected between an output terminal of the second output buffer and the first input of the input differential stage.
In an example, the plurality of feedback networks includes a fourth resistor feedback network including a third resistor connected between the output terminal of the first output buffer and a gate terminal of the first input transistor of the input differential stage; and a fourth resistor connected between the output terminal of the second output buffer and a gate terminal of the second input transistor of the input differential stage.
In an example, the instrumentation amplifier further comprises a current buffer stage including a pair of transistors, each of the pair of transistors being configured as a current source to a corresponding transistor of the folded cascode amplifying stage, the current buffer stage being configured to provide a portion of the sum of the output signals to input terminals of a folded cascode stage; and a dependent current source connected to the current buffer stage, the dependent current source being configured to provide cancellation current to input terminals of folded cascode stage.
Other variations and combinations of the embodiments in the summary section are with on the scope of the present disclosure.